University of Tehran Press Iranian Journal of Soil and Water Research 2008-479X 51 12 2021 02 19 Assessment of Soil Quality in Paddy Soils with Different Yields (A Case Study: Kouchsfahan, Guilan Province) Assessment of Soil Quality in Paddy Soils with Different Yields (A Case Study: Kouchsfahan, Guilan Province) 3161 3176 78556 10.22059/ijswr.2020.305420.668660 FA Maryam Shakouri PhD student, Department of Soil Science, Faculty of Agricultural Science, University of Guilan 0000-0001-7764-9578 Mahmoud Shabanpour Department of Soil Science, Faculty of Agricultural Science, University of Guilan Naser Davatgar Soil and Water Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Majid Vazifehdoust Assistant professor, Department of Water Engineering, Faculty of Agricultural Science, University of Guilan, Journal Article 2020 06 30 Rapid growth of population, followed by increasing food demand, necessitates knowledge of the relationship between yield and soil conditions. The soil quality index (SQI) is one of the indicators showing the soil conditions and the related properties very well.This study was performed to determine the effect of soil quality on rice yield in north of Iran (Gilan province). 64 soil samples from rice fields were prepared to measure the physical and chemical properties affecting soil quality and also the yield of rice in the mentioned fields were determined using plot. Then the total yields were divided into three classes with yields of less than 4000 kg/ha (first class), 4000-4500 kg/ha (second class) and more than 4500 kg/ha (third class). Among the studied properties, 16 properties as selected indicators of total data method (TDS) and five properties using principal component analysis as selected indicators of minimum data set method (MDS) were selected to determine the soil quality index. Fuzzy logic was used for scoring and the concept of communality index was used to weight the indicators and finally they were combined using weighted additive method. The results of quality index showed a positive and high correlation between TDS and MDS methods (R2 = 0.87). The results of correlation coefficient between yield and SQI by TDS method (R2 = 0.52) were higher than the SQI by MDS method (R2 = 0.28).  In the MDS method, simmilar to TDS method, there was an increasing trend in the SQI value of higher yield classes, but there is no significant difference between the second and third classes. The difference between soil quality and lower yields with MDS method is significant, but this difference is not significant at higher yield levels, because as the number of indicators decreases, the accuracy and sensitivity of soil quality assessment decreases. Rapid growth of population, followed by increasing food demand, necessitates knowledge of the relationship between yield and soil conditions. The soil quality index (SQI) is one of the indicators showing the soil conditions and the related properties very well.This study was performed to determine the effect of soil quality on rice yield in north of Iran (Gilan province). 64 soil samples from rice fields were prepared to measure the physical and chemical properties affecting soil quality and also the yield of rice in the mentioned fields were determined using plot. Then the total yields were divided into three classes with yields of less than 4000 kg/ha (first class), 4000-4500 kg/ha (second class) and more than 4500 kg/ha (third class). Among the studied properties, 16 properties as selected indicators of total data method (TDS) and five properties using principal component analysis as selected indicators of minimum data set method (MDS) were selected to determine the soil quality index. Fuzzy logic was used for scoring and the concept of communality index was used to weight the indicators and finally they were combined using weighted additive method. The results of quality index showed a positive and high correlation between TDS and MDS methods (R2 = 0.87). The results of correlation coefficient between yield and SQI by TDS method (R2 = 0.52) were higher than the SQI by MDS method (R2 = 0.28).  In the MDS method, simmilar to TDS method, there was an increasing trend in the SQI value of higher yield classes, but there is no significant difference between the second and third classes. The difference between soil quality and lower yields with MDS method is significant, but this difference is not significant at higher yield levels, because as the number of indicators decreases, the accuracy and sensitivity of soil quality assessment decreases. https://ijswr.ut.ac.ir/article_78556_4e47d223ce585b294d344f23626d0726.pdf